Insects cause over 22 billion dollars of crop damage in the United States alone. Many of the widely used insecticides are older neurotoxic compounds, and there is a substantial need for new, safer chemistries. Strain NRRL No. 30232 is a proprietary strain of Streptomyces galbus described in U.S. Pat. No. 6,682,925 that produces a group of closely related macrolides, called dunaimycins, exhibiting insecticidal activity, especially against Lepidoptera (caterpillars). Dunaimycins are 24-membered macrolides produced by actinomycetes that were first reported in the early 1990s by research groups at Abbott Laboratories. The Abbott researchers elucidated the structures of various dunaimycin species, A1, C1, C2, D2, D2S, D3 and D4S; studied their antimicrobial and immunosuppressive activities; and described the taxonomy of the producing organisms, two strains of Streptomyces diastatochromogenes. Karwowski, J. P., et al. Journal of Antibiotics December 1991, p. 1312-1317; Hochlowski, J. E., Journal of Antibiotics, December 1991, pp. 1318-1330; and Burres, N. S., et al., Journal of Antibiotics, December 1991, pp. 1331-1341. A few later publications described insecticidal or acaricidal activity of specific dunaimycins.
While the literature describes purification of specific dunaimycins and elucidation of their structure and activity, it lacks disclosures regarding interactions between the various species of dunaimycins and comparisons of insecticidal activity of the various dunaimycins. In addition, although production of fermentation broth containing dunaimycins in the gram per liter range is necessary to create a commercially viable insecticidal product, dunaimycin-related publications describe production of dunaimycins at milligram per liter levels. The background literature does not disclose methods for increasing dunaimycin production nor does it appreciate the corresponding challenges of scale-up.
In conducting experiments to increase dunaimycin production of Streptomyces galbus NRRL No. 30232 through screening of libraries of antibiotic-resistant mutants and optimizing fermentation conditions, Applicants increased dunaimycin production to previously unreported levels of at least 2.5 gram dunaimycin per liter fermentation broth (prior to concentration). Surprisingly, however, Applicants found that an increase in dunaimycin production was not necessarily proportional to an increase in insecticidal activity. Applicants analyzed in greater detail the interactions between the various species of dunaimycins and determined that particular dunaimycin species are insecticidally active, while others are either inactive or antagonistic to insecticidal activity.